Russia has ridiculed a UK minister for suggesting it could cause "thousands and thousands and thousands" of deaths by crippling British infrastructure.
Defence Secretary Gavin Williamson told the Daily Telegraph Moscow was spying on energy supplies which, if cut, could cause "total chaos" in the country.
But Russian Defence Ministry spokesman Igor Konashenkov said Mr Williamson had "lost his grasp on reason".
The comments were worthy of a Monty Python sketch, Mr Konashenkov added.
He accused Mr Williamson of trying to scare the British public in an effort to get more money for the armed forces.
The UK has four undersea energy connections for electricity linked to mainland Europe and a further four for gas.
Mr Williamson, who became defence secretary last November, said Russia had been researching these types of connections and would be willing to take action "any other nation would see as completely unacceptable".
He told the paper: "The plan for the Russians won't be for landing craft to appear in the South Bay in Scarborough, and off Brighton Beach.
"They are going to be thinking: 'How can we just cause so much pain to Britain?'
"Damage its economy, rip its infrastructure apart, actually cause thousands and thousands and thousands of deaths, but actually have an element of creating total chaos within the country."
It is a "real threat", he added.
Responding to the comments, Mr Konashenkov said Mr Williamson's "morbid fear" of Russian activities belonged in a children's comic book or an episode of Monty Python's Flying Circus.
"It would seem that in his fiery fight for banknotes in the defence budget, the British defence chief has lost an understanding of the boundaries of common sense," he said.
"For the minister's information, all data regarding the location of British power stations and pipelines is as secret as, for instance, photographs and the location of Westminster Abbey or Big Ben."
The warning comes after the chief of the National Cyber Security Centre, Ciaran Martin, said earlier this week that Russia had already staged attacks against Britain's media, telecommunications and energy sectors over the past year.
And head of the British army, Sir Nick Carter, has warned the UK is struggling to keep up with Russian capabilities.
The Ministry of Defence is under pressure to avoid cuts that could be coming from the Treasury.
Mr Williamson has already been told there could be a Tory revolt over reductions to army numbers and naval capability, and suggested he will be asking the chancellor for more money.